The red shift of an object
is directly measurable. The wavelength \(\lambda _{\rm e}\)  is fixed by
physics of the source, say, it is the wavelength of a photon
emitted by an excited hydrogen atom. So,
one identifies a series of emission
or absorption lines, thus determining \(\lambda _{\rm e}\) ,
and measures their actual wavelengths \(\lambda _0\) .
These spectroscopic measurements give accurate values of \(z\) 
even for distant sources. On the other hand, the red shift
is related to
the time of emission and hence to the distance to the source.
Absolute distances to astrophysical sources have a lot more systematic
uncertainty, and so do the direct measurements of the Hubble
parameter \(H_0\) .
According to the Planck Collaboration [1]},
the combination of observational data
gives
\(H_0 = (67.8 \pm 0.9)~\frac{\mbox{km}}{\mbox{s Mpc}} \approx (14.4 \times 10^9~\mbox{yr})^{-1} \; ,\) 
